1. Field of the Invention
The present invention relates to a method for removing carbon scale, or the so-called coke, which is apt to be formed in heating furnaces and reactors in chemical plants of the petrochemical industry, coal-chemical industry, etc.
2. Description of the Prior Art
In removing the carbon scale formed on the inside surface of material heating furnaces, or reactors such as the preheating portion or the reaction tube of a naphtha cracking system connected to the ethylene manufacturing equipment in a petrochemical factory, the conventional decoking method comprising introducing steam and air to the portion where the scale is formed while heating the body of the furnace or reactor up to a temperature of from 500.degree. to 700.degree. C. or thereabouts and thereby oxidizing the scale has been prevalent. In addition to this, the so-called hydrojet method wherein high-pressure water is blown against the scale through a nozzle thereby to exfoliate and remove the scale has also been adopted.
However, all these conventional methods involve various troubles. For instance, in the case of the decoking method employing the process of heat treatment at high temperature, there is a fear of causing damage to the furnace or reactor arising from the corrosion of the metallic material constituting the structure due to the high temperature. Besides, depending on the quality of the material of which the structure is built, it frequently happens that a method of treating at a high temperature such as from 500.degree. to 700.degree. C. is inapplicable from the view point of the resistance to corrosion of the material. Moreover, in the method of treating at such a high temperature as above, the processes of heating and controlling the temperature while avoiding infliction of damage on the structure and controlling the quantity of steam blown in, the dampness and other conditions for treatment are attended with considerable technical difficulties.
In the case of the hydrojet method, it is impossible to remove the scale formed in the bent tube portion as well as the following portion, and therefore, the reliability of its effect remarkably decreases depending on the structure of the plant. Besides, there are instances wherein the hardness of the carbon scale and the strength of the adhesion thereof render the removal of said scale impossible. In addition, the hydrojet method causes secondary problems with respect to the treatment of waste water that is discharged, disposal of the scale that is discharged thereby, and so on.